Reduction in myocardial acidosis using blood cardioplegia

Custodiol-N versus Custodiol: a prospective randomized double-blind multicenter phase III trial in patients undergoing elective coronary bypass surgery

OBJECTIVE

HTK-Solution (Custodiol) is a well-established cardioplegic and organ preservation solution. We currently developed a novel HTK-based solution, Custodiol-N, which includes iron chelators to reduce oxidative injury, as well as L-arginine, to improve endothelial function. In this first in-human study, Custodiol-N compared to Custodiol in patients undergoing elective coronary artery bypass surgery. The aim of this comparison was to evaluate the safety and ability of Custodiol-N to protect cardiac tissue.

METHODS

The study was designed as a prospective randomized double-blind non-inferiority trial. Primary end-point was area under the curve (AUC) of creatine kinase MB (CK-MB) within the first 24 h after surgery. Secondary end-points included peak CK-MB and troponin-T and AUC of troponin-T release, cardiac index, cumulative catecholamine dose, ICU-stay and mortality. All values in the abstract are given as mean ± SD, p < 0.05 was considered statistically significant.

RESULTS

Early termination of the trial was performed per protocol as the primary non-inferiority end-point was reached after inclusion of 101 patients. CK-MB AUC (878 ± 549 vs 779 ± 439 h* U/l, non-inferiority p < 0.001, Custodiol vs Custodiol-N) and troponin-T AUC (12990 ± 8347 vs 13498 ± 6513 h*pg/ml, noninferiority p < 0.001, Custodiol vs Custodiol-N) were similar in both groups. Although the trial was designed for non-inferiority, peak CK-MB (52 ± 40 vs. 42 ± 28 U/l, superiority p < 0.03, Custodiol vs Custodiol-N) was significantly lower in the Custodiol-N group.

CONCLUSION

This study shows that Custodiol-N is safe and provides similar cardiac protection as the established HTK-Custodiol solution. Significantly reduced peak CK-MB levels in the Custodiol-N group in the full analysis set may implicate a beneficial effect on ischaemia/reperfusion injury in the setting of coronary bypass surgery.

Intraoperative metabolic monitoring of the heart: II. Online measurement of myocardial tissue pH

Under conditions of ischemia, the hydrogen ion [H+] accumulates in the myocardial tissue in proportion to the magnitude of the ischemic insult. The accumulation of [H+] is the result of both increased anaerobic production of [H+] secondary to decreased substrate and decreased washout of [H+] secondary to decreased coronary perfusion. The Khuri tissue pH electrode/monitoring system has been developed and validated over the past two decades. Its scientific basis and correlates have been established, and it is the only system that has been approved for use in humans. Myocardial tissue pH has been monitored in the anterior and posterior walls of the left ventricle in more than 700 patients undergoing major cardiac surgery. An understanding of the relationship between pH and temperature and between the pH and [H+] in tissues is important for the proper interpretation of the myocardial pH data generated in the course of an operation. Intraoperative monitoring of myocardial pH is the only modality available to the cardiac surgeon for online assessment and improvement of the adequacy of myocardial protection. By defining myocardial protection in terms of protection from myocardial tissue acidosis, this technology provides a new tool with which the comparative efficacy of the various myocardial protection techniques can be assessed. It also provides an online tool for assessing the adequacy of coronary revascularization, and has the potential of improving procedures and outcomes for off-pump coronary artery bypass grafting.

Proper timing of blood cardioplegia in infant lambs: superiority of a multiple-dose regimen

BACKGROUND

In the pediatric and infant age groups, it is unclear whether repeated infusions of blood cardioplegia solution during ischemic arrest are beneficial or detrimental when compared with a single-dose regimen.

METHODS

Twenty lambs (aged 6 to 7 weeks) were placed on cardiopulmonary bypass. A miniature glass-tip electrode measured myocardial pH and hydrogen ion concentration, [H+], in the anterior wall. The aorta was clamped for 2 hours. Group S (n = 10) received a single dose of blood cardioplegia solution. Group M (n = 10) received multiple doses of blood cardioplegia solution at 20-minute intervals.

RESULTS

The amount of [H+] generated during the cross-clamp period was greater in group S than in group M (39.2 +/- 10.1 nmol/L versus 0.4 +/- 1.4 nmol/L, p < 0.008). The percent increase in the time constant, tau, an index of diastolic relaxation, was more prolonged after cardiopulmonary bypass in group S when compared with group M (51.4% +/- 2.8% versus 6.4% +/- 3.0%, p < 0.0001). Similarly, the percent decrease in end systolic elastance, a measure of systolic contractility, was greater in group S after cardiopulmonary bypass when compared with group M (29.5% +/- 1.4% versus 7.3% +/- 1.3%, p < 0.0001).

CONCLUSIONS

In this infant lamb model, multiple doses of blood cardioplegia solution provided superior metabolic preservation and hemodynamic support after 2 hours of aortic clamping when compared with a single-dose regimen.

Interstitial pH during myocardial preservation: assessment of five methods of myocardial preservation

We investigated changes in myocardial pH during cardioplegic arrest with five methods of preservation at 15 degrees +/- 1 degree C. Twenty-five dogs were subjected to cardiopulmonary bypass for 150 minutes. Group I (control) had hypothermia only. Group II received THAM-buffered blood cardioplegia, group III a bicarbonate-buffered blood cardioplegic solution, group IV infusions of hyperkalemic blood, and group V oxygenated St. Thomas 2 solution. After 120 minutes of ischemia, interstitial pH in group I was markedly depressed (6.4 +/- 0.07; p < 0.01). The pH in groups II and IV was well maintained (7.23 +/- 0.05 and 7.27 +/- 0.07) and differed significantly (p < 0.05) from that of the remaining groups. The pH in groups III and V was less well maintained (7.14 +/- 0.02 and 7.01 +/- 0.05), with no significant difference (p > 0.05) between these two groups. Postreperfusion functional recovery after 45 minutes was 24% +/- 6% in group I, 92% +/- 3% in group II, 82% +/- 5% in group III, 84% +/- 4% in group IV, and 66% +/- 6% in group V. Creatine kinase levels were significantly (p < 0.01) increased and ultrastructural damage was more prominent in group I compared with the remaining groups. Myocardial water content significantly increased in all groups. We conclude that a strongly buffered blood-based cardioplegic solution is more effective in preventing interstitial acidosis during moderate hypothermia and that maintenance of an optimal tissue pH plays an important role in postischemic functional recovery.

Blood cardioplegia: a review and comparison with crystalloid cardioplegia

The Oxford International Symposium on myocardial preservation provided an appropriate milestone and impetus to survey one aspect of operative myocardial preservation, namely blood cardioplegia, and to contrast it with the more popular crystalloid cardioplegia. This review is by no means complete or exhaustive but represents my best effort to summarize important information that has accumulated in the literature as blood cardioplegia, and our understanding of it, has evolved. It is appropriate to compare blood and crystalloid cardioplegia with respect to biochemical and physiological differences. Clinical comparison has been limited, for the most part, to randomized studies, and a number of differences and details of clinical management of the two techniques have been omitted, either because they seemed unimportant or there was no good information that would allow an objective comparison of their significance. Hopefully, the reader will recognize the intent to focus on meaningful differences and similarities between the two techniques and to present them fairly.

Upgrading acellular to sanguineous cardioplegic efficacy

To determine which biochemical entity of the red cell is responsible for preventing augmented postischemic myocardial oxygen consumption (MVO2), 28 canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work (SW) and MVO2 during incremental volume loading on right heart bypass before and 30 min after 2 hr of 10 degrees C cardioplegic arrest with unmodified oxygenated crystalloid cardioplegia (OC), OC with histidine of equal buffering capacity as 18% hematocrit blood (OC + H), or OC with 200 units/ml of superoxide dismutase and catalase (OC + SOD/C). In all groups, the slope of the linear SW vs end-diastolic volume relationship, Mw, and the slope of the linear SW vs MVO2 relationship, Me, were unchanged after cardioplegic arrest. The intercept of the SW vs MVO2 relationship, Eo, was augmented an average of 22.2% in the OC group, but both OC + H and OC + SOD/C prevented this subtle expression of ischemic injury. The characteristic of the red cell most likely responsible for the myoprotective efficacy of blood cardioplegia is buffering capacity; however, since the effects of tissue acidosis are partially mediated by free radicals, the use of free radical scavengers can also ameliorate ischemic damage incurred during cardioplegic arrest.

Reducing intraoperative myocardial acidosis by continuous cardioplegic perfusion via the coronary sinus

Continuous retrograde coronary sinus perfusion (RCSP) can deliver cardioplegic solution homogeneously to the myocardium via the disease-free venous system. However, administration of cardioplegic solution through the coronary venous system necessitates low pressure infusion which may limit the rate of cardioplegic delivery. In addition, infusion of the solution at low flow rates may not prevent the development of myocardial acidosis during arrest. To determine if RCSP is capable of limiting intraoperative myocardial acidosis, open-chest pigs, monitored by intramyocardial pH probes, underwent cardioplegic arrest with a single dose aortic root infusion followed by a 45-min period of no RCSP (Group 1), RCSP of 25 mEq/liter bicarbonate-buffered cardioplegic solution (Group 2), RCSP of blood-buffered cardioplegic solution (Group 3), and RCSP of histidine-buffered cardioplegic solution (Group 4). There were no significant differences between the groups with respect to baseline pH, with a range of 7.27 to 7.32. At the end of the 45-min arrest period, Group 2 had a statistically higher pH, 7.06 +/- 0.08, compared to Group 1, 6.74 +/- 0.08 (P less than 0.05). Hearts in Groups 3 and 4 demonstrated preservation of preischemic pH levels after 45 min of arrest, 7.29 +/- 0.07 and 7.37 +/- 0.10, respectively, significantly higher than either Group 1 or 2 (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)